1. Field of the Invention
This invention relates generally to fiberoptic catheters and more specifically to laser catheters such as those used in angioplasty.
2. Background of the Invention
A surgical procedure commonly referred to as coronary angioplasty is well known in the art and is a noninvasive technique which addresses problems associated with the blockage and sometimes occlusion of coronary arteries. In this procedure, a guide catheter is typically introduced into the femoral artery in the leg and directed upwardly through the aortic arch into either the left coronary artery or the right coronary artery.
A very small guidewire is typically introduced through the guide catheter and carefully directed through the smaller coronary arteries up to and typically across the lesion of interest. An operative catheter is introduced over the guidewire and interiorly of the guide catheter until its distal end is brought into proximity to the lesion. The next step in the surgical procedure depends on the nature of the operative catheter. Balloon catheters have been used to compress the plaque, but more recently, laser catheters have been used to ablate the plaque material to increase the patency of the artery.
Laser catheters rely upon optical fibers to transmit laser energy from the proximal end of the catheter to the distal end of the catheter. In the past this transmission has taken place through a fiberoptic which may comprise a single fiber or a bundle including many small fibers which are arranged in a generally parallel configuration.
Although the laser catheter relies heavily on the guide catheter and the guidewire for manipulation, it nevertheless must have its own flexibility in order to negotiate the various bends and curves which define a typically torturous path to the lesion. It is the bending of the optical fibers that has presented particular problems for these laser catheters.
In the past, the parallel fibers have typically been housed in a catheter jacket. When the catheter is bent, the parallel fibers have unequal bending paths. With an outer jacket closely spaced to the fiber bundle, the catheter would have a very high resistance to bending due to the restriction of movement. It has been found that this resistance can be decreased by providing some space between the fiber bundle and the catheter jacket. This space increases the ability of the fibers to move relative to each other as required when the catheter is bent. Unfortunately, in an environment wherein catheter diameter is particularly critical, any provision of space to accommodate bending is provided only at a great sacrifice to catheter size.
These catheters of the past have typically been constructed by inserting the delicate fibers into one end of the catheter jacket. Attempts to coextrude the fibers and jacket have not provided the requisite space to facilitate bending of the catheter.
The bending of parallel fibers has other undesirable mechanical consequences. The fibers on the interior edge of the curve are placed in compression and tend to move away from the jacket toward the axis of the catheter. In contradistinction, the fibers on the outside of the curve are placed in tension, but they also tend to move away from the jacket toward the axis of the catheter. This results in a flattening of the catheter along the curve. While the flattening produces a reduction in the catheter width in the plane of the curve, this reduction in width is necessarily accompanied by a corresponding expansion of the catheter width in a direction perpendicular to the plane of the curve. Thus a catheter that has a specific diameter tends to increase in size when it is bent or curved. In some cases this increase is sufficient to cause the laser catheter to bind on the inner surface of the guide catheter.
In all cases, this expansion problem results in increased resistance to movement of the laser catheter within the guide catheter. This cannot be tolerated in a surgical procedure as delicate as angioplasty. As the surgeon moves the laser catheter through the arteries, any resistance to movement is relied on to convey information as to resistance at the distal tip not increased friction along the catheter wall. Using a longer guide catheter to reduce friction is surgically undesirable.
Another problem associated with the parallel orientation of optical fibers has been their general inability to transmit torque from the proximal end of the catheter to the distal end of the catheter. In order to add torsional rigidity to the catheter, it has been necessary to provide a large torque wire or a metallic braid along the entire length of the catheter. This of course has either increased the size of the catheter or consumed space which would otherwise be available within the catheter.
These attempts to solve the problems of the prior art have left a requirement for a fiberoptic catheter having greater flexibility and torque transmission characteristics, reduced diameter and bending stresses, without any sacrifice to size or interior space.